Summary: at very negative potentials, the lock-open currents were normalized to the current level in
the control case for comparison. To estimate the K1/2 of the blockers, the amount of block
was estimated by isochronal comparison of the scaled traces.
In the single-channel recordings, the leak current and capacitative transients were
subtracted with an idealized fit to a blank trace. Traces were filtered at 1 kHz, sampled at
2 kHz.
The rates of recovery of Shaker V474C from block by Cd2þ
by DMPS were measured as
the single exponential fit of the current as a function of the cumulative exposure at the test
voltage. The test pulses were adjusted in length so that the time constant of recovery
would be equal to at least two pulse durations. These single exponential rates were
plotted versus voltage. Because of the large variation in the g-V midpoint for each
experiment, the voltage of the recovery was corrected for the g-V midpoint of the
individual experiment13
: Vcorrected ¼ V þ (Vmid 2 Vmid). The average Boltzmann fit of
the g-Vs is plotted.
Received 20 November 2003; accepted 4 March 2004; doi:10.1038/nature02468.
1. Jiang, Y. et al. The open pore conformation of potassium channels. Nature 417, 523­526 (2002).
2. Doyle, D. A. et al. The structure of the potassium channel: molecular basis of Kþ
conduction and